Autobuild: Clarify README regarding system modifications

.github/autobuild/README.md

@@ -4,4 +4,7 @@ The scripts in this folder are used by the Github autobuild actions in .github/w
 They are responsible for setting up the Github environment, building the binaries and passing the resulting artifacts back to the workflow.
 
 The scripts may work outside of Github, but haven't been designed or tested for that use case.
+Some of the scripts modify global system settings, install software or create files in directories which are usually managed by package managers.
+In short: They should probably only used in throw-away environments.
+
 See the various platform-specific build scripts in their own folders for standalone builds (e.g. windows/deploy_windows.ps1).